Establishment of Geodetic Coordinate Systems - Geodesy: Introduction to Geodetic Datum and Geodetic Systems - page 376

coordinates of 48,919 first- and second-order astro-geodetic points were
obtained with an average accuracy of position of 0.11 m, which bettered the

precision and current situation of the national astro-geodetic networks and
improved the density and distribution of the CGCS2000 reference frame.

Difference Between CGCS2000 and ITRF

By definition, CGCS2000 and ITRF belong to the same coordinate system. The
coordinates of CGCS2000 are determined by GPS relative positioning techniques,
while the datum station coordinates are in the ITRF reference frame. Hence,
CGCS2000 and ITRF belong to the same reference frame. With proper observa-
tions and reasonable calculations, we can strive to keep CGCS2000 consistent with
ITRF within 2 cm. Hence, CGCS2000 is the Chinese equivalent to ITRF but of a
higher density. The difference between CGCS2000 and ITRF is negligible when the
accuracy is at the level of a centimeter.

Difference Between CGCS2000 and the Current Local Coordinate
System

Different Methods for Ellipsoid Orientation

A local coordinate system is designed to establish the ellipsoid that best fits the
geoid over the local area by means of an astro-geodetic orientation, whose origin
deviates considerably from the geocenter (approximately 200 m). Taking XAS80 as
an example, its reference ellipsoid fits the geoid well on a national basis. Two
isolines of zero height anomalies pass through the east and west of China. The
height anomalies in most areas are within 20 m. The effect of the height anomalies
on distance is smaller than 1/300,000. CGCS2000 is a geocentric coordinate
system, which is realized by modern geodetic techniques based on the techniques
employed in the establishment of a terrestrial reference frame. The center of the
ellipsoid defined by CGCS2000 is coincident with the Earth's center of mass.
Meanwhile, the ellipsoid also most closely fits the geoid on a global basis. The
ellipsoids that are global “best fits” to the geoid may not necessarily be local “best
fits” to the geoid.

Different Realization Techniques

The local coordinate system is established by classical geodetic techniques,
whereas CGCS2000 is established by space geodetic techniques.